Yes, I get that happening to me every once in a while. What's even weirder, is when I'm in sync with my wife like that - we both have the same tune in our heads and it's only revealed when one of us breaks out vocally with the song - cue spooky music.

I hear you. That happened to me once. I was driving around town with a buddy of mine (keyboardist). When had been listening to some Zappa earlier. Anyway, it's perfectly quiet in my car and we both, in near perfect unison, sing a line from Greggery Peccary, the one where Greggery is in the office and the chorus goes "yoo-yoo yoo yoo-yoooo". We just stopped and looked at each other. It was freaky. Obviously there was something that cued us both to start thinking of the song at the same point at the same time, and for whatever reason, we both vocalized that line.